Electronically controlled railway vehicle-type brake systems, as is generally well known in the art, have been in widespread use in the passenger transit-type railway industry for several years. More recently, however, these electronically controlled railway vehicle brake systems as well as a number of other electronic-type control systems have been installed on the modern freight-type railway locomotives in order to provide improvement in not only the performance of such brake systems but also the reliability of these brake systems.
Such modern-day locomotive electronic controls, which includes the locomotive brake control systems, will normally have state of the art computer technology incorporated therein. Such computer technology enables both a reduction of the extensive hardware requirements and it will more easily facilitate the adaptation of the different electronically controlled systems to various customer requirements.
In one such electronically controlled brake control system, which is illustrated and described in U.S. Pat. No. 5,222,788 and assigned to the same assignee as the present invention, there is provided a cab-mounted, handle-operated brake controller assembly. Such handle-operated brake controller assembly will output the desired brake command electrical signal to a microprocessor unit. Such microprocessor unit, in this particular brake control system, will then interpret the brake command electrical signal received in terms of a feedback signal. This feedback signal is representative of the air pressure contained in an equalizing reservoir of such brake system. After this feedback signal is received, such microprocessor unit will then effect an appropriate operation of the application and release electropneumatic valves in order to adjust the equalizing reservoir air pressure in accordance with the interpretation made of such brake command electrical signal. In another such electronically controlled brake system taught in U.S. Pat. No. 5,332,297 to Cunkelman et al., there is illustrated and described a microprocessor based locomotive brake control system that features both an electropneumatic brake pipe pressure regulating circuit through which pressure in the brake pipe is controlled and a normally closed charging cutoff valve between that regulating circuit and the brake pipe. The assignee of U.S. Pat. No. 5,332,297 is also the assignee of the present invention. The teachings of U.S. Pat. No. 5,332,297 are also incorporated herein by reference.
A relatively high-capacity pneumatic relay valve device is employed in this particular electronically controlled brake system so that the trainline brake pipe air pressure can be varied in accordance with the variations of the equalizing reservoir air pressure, in order to control the brakes disposed on the railway cars. This so-called prior art type brake pipe control circuit of the afore-mentioned electronically controlled brake system has been illustrated and described in U.S. Pat. No. 4,904,027, which is likewise assigned to the same assignee as the present invention. The teachings of U.S. Pat. No. 4,904,027 are, likewise, incorporated herein by reference thereto.
The electronic brake control system further includes a locomotive brake cylinder control circuit. Such brake cylinder control circuit includes both electropneumatic application and release valves. The electropneumatic valves, of such locomotive brake cylinder control circuit, are operated by the microprocessor unit in response to changes in brake pipe air pressure initiated by the brake pipe control circuit in accordance with movement by the operator of an automatic brake handle disposed on the cab brake controller unit.
Another relatively high-capacity pneumatic-type relay valve device is provided in this electronic brake control system in order to control the air pressure present in the locomotive brake cylinders in accordance with the pressure output signal of the locomotive brake cylinder control circuit application and release electropneumatic valves.
The electropneumatic valves present in both the brake pipe control circuit and the locomotive brake cylinder control circuit are arranged in such a manner to assume a pressure release state, in the undesirable event of a power loss at the microprocessor unit. As a consequence of such a power loss, therefore, the brake pipe air pressure is reduced while, consequently, the locomotive brake cylinder air pressure is released.
A pneumatic-type back-up control valve device is provided in the railway locomotive automatic brake control circuit in order to establish locomotive brake cylinder air pressure in response to the afore-mentioned reduction of brake pipe air pressure which results from such fail-safe operation of the electropneumatic valves in the brake pipe pressure control circuit, there being a double check valve arrangement provided in order to separate the pneumatic backup control valve device from the electropneumatic valves in the locomotive brake cylinder control circuit.
There are additional electropneumatic valves which are employed in conjunction with a charging cut-off valve device in a branch pipe via which the brake pipe air pressure control circuit is connected to the locomotive brake pipe. The charging cut-off valve device is provided in the system in order to establish the required communication link between the brake pipe air pressure control circuit and the brake pipe when the locomotive is to be set up for a "lead" operation, i.e., as the controlling locomotive, and to interrupt such communication link when the locomotive is to be set up for a "trail" operation, i.e., as a non-controlling locomotive.
The afore-mentioned charging cut-off valve device is a bistable valve and will, therefore, remain in its set position in the event of an undesirable microprocessor unit malfunction that results in a loss of power. In the event such an undesirable malfunction occurs on a controlling "lead" locomotive that is subsequently downgraded to a non-controlling "trail" status, it will be appreciated that the charging cut-off valve device will remain in its previously set open position. Typically, as is known in the railway industry, such a non-controlling locomotive is hauled "dead", i.e., without electrical power. Without such electrical power the application and release electropneumatic valves in the brake pipe air pressure control circuit are obviously de-energized. This condition will in turn cause the relay valve in this control circuit to assume an exhaust condition, thereby venting air pressure from the brake pipe by way of the open charging cut-off valve device. Accordingly, the needed ability to recharge the brake pipe with air pressure from another controlling "lead" locomotive, following a "loss of power" brake application, could be seriously jeopardized.
For a number of reasons, which are believed to be obvious from the above discussion, safety rules and regulations which govern the railway industry dictate that certain critical aspects of these electronically controlled railway vehicle-type brake systems must be tested at least periodically in order to determine that they are in proper working order. Such testing will normally be carried out at the time such freight-type railway locomotive is required to be in the shop for either some necessary repairs or any other routine maintenance requirements.
Prior to the present invention, when such required testing of the electronically controlled railway vehicle brake system was carried out, as is known by applicant, it was necessary for the brake system control unit to be physically removed from the cab of the locomotive prior to testing. However, as will become readily apparent to persons skilled in the railway vehicle braking art from the detailed description of the instant invention, there exists the possibility that certain aspects of this test might not be valid. For example, if the actual fluid pressures which are available to the various pressure communication lines on the locomotive are not at the desired and/or required pressure this undesirable condition may never be recognized when the electronic brake control system has been removed from the locomotive prior to such testing being performed.